1. Field of the Invention
This invention relates to a liquid supply device.
2. Description of the Related Art
Dust, such as rubbish and trash, frequently gets into a liquid medium which is supplied to a liquid reservoir to contaminate the reservoir. Thus, there has been conventionally used a liquid supply device that is equipped with a mesh filter, for excluding the dust from the liquid medium, in a supply passageway through which the liquid medium is supplied to the liquid reservoir, thereby supplying only the liquid medium into the liquid reservoir while excluding the dust.
The liquid supply device as described above will be hereunder described in detail (with reference to FIG. 4) in the case of an ink supply device 50 used for a ink jet printer.
The ink supply device 50 comprises an ink tank 46 for storing supplied ink 43a, a pump 47 for drawing the ink 43a stored in the ink tank 46 into a cylinder 52, through a check-valve 51a, by driving a piston 53. The ink 43a is pushed from the cylinder 52 through a check-valve 51b into a tube 49 which serves to guide the ink 43a to an ink reserving chamber (hereinafter referred to as "ink reservoir") 44 of an ink jetting head 40. An ink filter 48 for removing dust from the ink 43a, which is guided by the tube 49 and supplied into the ink reservoir 44, is located at the end of tube 49 and at the entrance to ink reservoir 44.
The ink jetting head 40 of the ink jet printer, to which the ink is supplied by the ink supply device 50, is formed with an orifice 41 having about a 50-micron diameter. The ink stored in the ink reservoir 44 is ejected through the orifice 41 by vibration of a piezo-vibrator 42.
When the ink 43 stored in the ink reservoir 44 is contaminated by dust, the orifice 41 becomes choked with the dust to degrade the printing operation. Accordingly, the ink reservoir 44 is supplied with the ink 43 that has been filtered to remove the dust to improve the printing operation. The ink reservoir 44 communicates with the atmosphere through an air filter 45. Thus, the inside of the ink reservoir 44 is kept at approximately atmospheric pressure to stabilize the ink supply thereto. In addition, dust in the atmosphere is prevented from contaminating the ink 43 of the ink reservoir 44 by air filter 45.
On the other hand, in order to surely exclude dust, whose particle size exceeds the size of the orifice 41, the ink filter 48 is so designed as to have holes of about 10-micron size. Therefore, it takes a long time for the ink 43 to pass through the ink filter 48. If the ink supply speed of the ink 43 which is supplied into the ink reservoir 44 is lower than the speed at which the ink 43 is consumed by the printing operation, then a point will be reached where there is no ink 43 in the ink reservoir 44 and the printing operation will be interrupted until the ink 43 can be sufficiently supplied to the ink reservoir 44.
In order to prevent this interruption of the printing operation, in the conventional ink supply device 50, the ink 43 is rapidly passed through the ink filter 48 by the use of a pumping force of the pump 47.
Therefore, in order to rapidly pass the dust-excluded liquid ink 43 into the ink reservoir 44, the conventional technique has required a device such as the pump 47, or the like, for rapidly passing the liquid ink with a resultant complicated structure.
In addition, there is a requirement for a power source for driving a device such as the pump 47 or the like. There is another problem in that the size of the structure of the ink jet printer can not be miniaturized due to the necessary driving mechanism for the piston (not shown) and the pump 47 having to have a driving source.